The present invention relates to a novel optical information recording member, methods for preparing such member and to methods of using such a member. In particular, the present invention relates generally to a high density information storage medium suitable for use with optical recording and playback methods and apparatus.
It is known in the prior art to construct optical recording members wherein a laser beam is selectively focused on the surface of the recording member to cause minute melted depressions or deformations in the surface of the recording film. In recording binary data on such an optical recording member, the melted depressions or deformations correspond to bits of information of one's and zero's. Such recorded information can be optically read out at a later time by various known means typically by a second or the same laser beam. Due to the extremely small size of the focused laser beam which is used, a very large amount of information can be recorded on a given area of such an optical recording member. For example, it has been reported that over four million individual bits of binary data have been recorded per square inch of record surface. With such a storage capacity or memory capacity it is clear that devices incorporating this have great utility.
Suitable devices have taken the form of multi-layered optical recording members which are typically made of a reflecting substrate, a layer of dielectric spacing material, and an absorbing imaging layer. Since the imaging layer must be deformed or melted in an extremely short period of time with limited power input, they typically are very thin. Being so thin they are typically sensitive to physical damage by mechanical contact and other devices including the users fingerprints. To protect the imaging layer in such configurations, it has been the practice to either overcoat them or provide a sandwich type configuration. In the air sandwich, the imaging surface is protected from environment attack and physical damage by two relatively thick transparent substrates bonded together within an annular spacer. This structure protects the surface against external surface dust, scratches and fingerprints which are separated from the imaging layer by more than about one millimeter and thus are displaced from the focal plane and so do not contribute to noise and bit errors. In addition, the recording sensitivity of the unprotected surface is preserved. Construction of an air sandwich structure however, requires a great deal of materials engineering relative to substrate and cap materials and adhesive bonding.
In the overcoating approach the imaging layer is protected from direct mechanical contact and thereby mechanical damage is limited by a rather thin transparent layer of an organic polymer or by an even thinner layer of a refractory inorganic such as silica. While this technique can be successful in protecting the device, it suffers the difficulty that recording sensitivity is often degraded. In addition, contaminants on the surface of the protective layer are not separated from the imaging plane by a distance great enough to not contribute to noise and bit errors.